The invention at hand, in which Mr. Claude Chekroun, Mr. Yves Michel, and Mr. Henri Sadones have had a part, concerns a process for attenuating or canceling certain side lobes of a microwave antenna pattern, as well as the application of this process to the elimination of the effects of active or passive interferences (jammers, ground clutter, sea clutter, etc.) at the time of reception on the antenna, and also to the detection and localization of several jammers liable to blind the antenna at reception, and also the applications of this process to the partial and local attenuation at reception by an antenna.
It is possible to improve the level of side lobes of microwave antennas, by trying, on the one hand, for electronic scanning antennas, to multiply the number of radiating elements of the antenna and the possible values of phase shift; and, on the other hand, for all types of antennas, to use components having very tight mechanical and radioelectric tolerances.
It is, as a matter of fact, presently being studied how to attenuate or cancel certain side lobes of a microwave antenna pattern of the electronic scanning type to create "notches" (or "holes" or "zeros") at reception, in the direction of these lobes. To do this, either one modifies the phase and amplitude of each radiating element of the antenna in order to create the "notches" or one combines several elementary elements of the antenna that one switches in opposite phase with the energy received, in the direction of the side lobe in question.
These methods have fundamental disadvantages:
They require a very considerable number of drivers, and, therefore, involve a considerable cost and a long switching time and this, all the more as the size of the antenna is increased.
They require a long switching time, on the order of about ten to one hundred microseconds, to achieve the attenuation or cancellation of a secondary lobe in a given direction, which means that when one uses this process to eliminate the effect of a jammer the antenna is, during the switching time, blinded by the jammer and is, therefore, in danger of losing the target followed by the radar. In the case where one combines several radiating elements, this method monopolizes a zone of the antenna that, instead of taking part in the whole of the function serves only to create a "hole" at reception (if one wishes to create several "holes", the monopolized zones are more numerous, which implies a limitation of 2 or 3 "holes" at reception).
Recently another method as well, which is in the process of development, is being suggested which consists of associating with the principal directive antenna a secondary antenna which is considerably less directive and to subtract from the signals received by the principal antenna those received by the secondary antenna. The gain of the secondary antenna being noticeably constant for all directions of surveyed space, the energy received from a possible jammer would be of the same order of magnitude as that coming from the target in the secondary antenna, which is not the case for the principal antenna in which the gain in the direction of the jammer is weak. By a spatial correlation, it is possible, in this manner, to minimize the noise brought in at the level of the antenna by an active or passive jammer.
This method has many disadvantages: it is not completely adaptive; the signal received from the target is appreciably reduced from the moment of the first subtraction; this method cannot be used for more than two jammers. It is very costly because it requires an auxiliary antenna and its concommitant processing for each external interference.
This process, that is the object of this invention, completely avoids the disadvantages of the above-mentioned methods, that is:
It uses a considerably smaller number of drivers than the other methods, for an antenna of the same size.
It uses elements completely exterior to the antenna, and, therefore, no zone of the antenna is monopolized.
It does not require an auxiliary antenna. It is, therefore able to be used for several simultaneous jammers, without the antenna pattern being deformed in any appreciable way outside of the zones involved.
The speed of the process is such that a given secondary lobe can be attenuated or canceled by switching requiring a matter of time on the order of ten nanoseconds. One can immediately see the advantage of a process than can cause an attenuation or "hole" at reception by the antenna in any direction whatsoever even before the echo received from the target has returned to the antenna.
Moreover, to carry out this process, one uses, as one will see, an extremely simple technology and a very small number of drivers, which gives any resulting applications a great advantage in the areas of technological simplicity, simplicity of implementation and of drivers, as well as lower cost.
Finally this process may be applied to any antenna, be it mechanical scanning or electronic scanning.